[PATCH net-next v6 02/12] net/rds: undo conn_alloc() the same way on every __rds_conn_create() exit

[Allison Henderson <achender@kernel.org>]

trans->conn_alloc() may allocate transport data for every path of a
multipath connection - rds_tcp_conn_alloc() does - which is why the
lost-creation-race exit of __rds_conn_create() loops over all npaths
when it frees the connection it just built.  The passive-connection
exit right above it frees only path 0.

That is not a leak today: a passive twin is only created for an IB
loopback connection (an incoming TCP connect to a local address is
refused with -EOPNOTSUPP before it gets here), and the IB transport is
not multipath, so npaths is 1 on that exit.  But the two exits express
the same "undo conn_alloc()" step in two different ways, and the
following patches add another exit of the same kind.  Move the loop
into a helper and use it everywhere, so that the step cannot silently
diverge if a multipath transport ever grows a passive twin.

Assisted-by: Claude-Code:claude-fable-5
Signed-off-by: Allison Henderson <achender@kernel.org>
---
 net/rds/connection.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/net/rds/connection.c b/net/rds/connection.c
index b6c4beb50eaf..a96569a3ee9a 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -161,6 +161,22 @@ static void __rds_conn_path_init(struct rds_connection *conn,
 	cp->cp_flags = 0;
 }
 
+/* Undo trans->conn_alloc(): it may have allocated transport data for
+ * every path of a multipath connection, not just for path 0.
+ */
+static void rds_conn_free_transport_data(struct rds_connection *conn,
+					 int npaths)
+{
+	struct rds_conn_path *cp;
+	int i;
+
+	for (i = 0; i < npaths; i++) {
+		cp = &conn->c_path[i];
+		if (cp->cp_transport_data)
+			conn->c_trans->conn_free(cp->cp_transport_data);
+	}
+}
+
 /*
  * There is only every one 'conn' for a given pair of addresses in the
  * system at a time.  They contain messages to be retransmitted and so
@@ -316,7 +332,7 @@ static struct rds_connection *__rds_conn_create(struct net *net,
 	if (parent) {
 		/* Creating passive conn */
 		if (parent->c_passive) {
-			trans->conn_free(conn->c_path[0].cp_transport_data);
+			rds_conn_free_transport_data(conn, npaths);
 			free_cp = conn->c_path;
 			kmem_cache_free(rds_conn_slab, conn);
 			conn = parent->c_passive;
@@ -332,18 +348,7 @@ static struct rds_connection *__rds_conn_create(struct net *net,
 		found = rds_conn_lookup(net, head, laddr, faddr, trans,
 					tos, dev_if);
 		if (found) {
-			struct rds_conn_path *cp;
-			int i;
-
-			for (i = 0; i < npaths; i++) {
-				cp = &conn->c_path[i];
-				/* The ->conn_alloc invocation may have
-				 * allocated resource for all paths, so all
-				 * of them may have to be freed here.
-				 */
-				if (cp->cp_transport_data)
-					trans->conn_free(cp->cp_transport_data);
-			}
+			rds_conn_free_transport_data(conn, npaths);
 			free_cp = conn->c_path;
 			kmem_cache_free(rds_conn_slab, conn);
 			conn = found;
-- 
2.25.1